The zebra mussel, a freshwater shellfish native to Eastern Europe, has long been spreading out from its original habitats and has now reached parts of North America. There are reasons to believe that this invasion cannot be stopped and that it poses a serious threat to freshwater fish populations in all of North America.
First, the history of the zebra mussel's spread suggests that the invasion might be unstoppable. It is a prime example of an invasion made possible by human transportation. From the zebra mussel，s original habitats in Eastern Europe, ships helped spread it out along new canals built to connect Europe’s waterways. The mussel can attach itself to a ship’ s bottom or can survive in the water—called "ballast water"—that the ship needs to take on to properly balance its cargo. By the early nineteenth century, the mussel had spread to the whole of Europe. It was later carried to the east coast of North America in the ballast water of ships traveling from Europe. The way ships have spread the zebra mussel inthe past strongly suggests that the species will soon colonize all of North America.
Moreover, once zebra mussels are carried to a new habitat, theycan dominate it. They are a hardy species that does well under a variety of conditions, and they have a high rate of reproduction. Most important, however, zebra mussels often have no predators in their new habitats, and species without natural predators are likely to dominate their habitats.
Finally, zebra mussels are likely to cause a decline in the overall fish population in habitats where they become dominant. The mussels are plankton eaters, which means that they compete for food with manyfreshwater fish species.
The writer and the speaker have a debate on the effect of zebra mussel on freshwater fish populations in North America. The writer believes that it exerts a serious threat and cannot be stopped， while the speaker holds an opposite view.
First， the writer states that history has seen zebra mussel spread by attaching itself to a ship’s bottom or survive in ballast water. However， the speaker thinks it’s incorrect to project this history into the future. There are effective ways to stop ships from carrying the zebra mussels across the ocean. For example， ships take on fresh ballast water in Europe and then empty it into North American waterways on arrival， full of zebra mussels. But the ships can empty out the freshwater and refill with ocean water when they are still out in the ocean. In this way， the zebra mussel problem will be settled.
Second， the writer points out that as a hardy species， zebra mussels can easily dominate new habitats without any natural predators. In accordance with the speaker， this claim does not hold water. No predator happens only in the beginning. In Europe local aquatic birds sooner or later come to notice a new food source and switch from old habits to eating zebra mussels. So it is unlikely for zebra mussels to dominate new habitats.
Lastly， the writer mentions that zebra mussels will have a destructive impact on fish population in new habitats because as plankton eater， they outcompete other fish for food. By contrast， the speaker contradicts the overall decline theory. According to him， despite the negative effect on plankton， the mussels generate nutrients that can be eaten by fish near the bottom of the lake or river. So bottom-feeding fish populations will grow while plankton eating fish population shrinks.
Transition Words or Phrases used:
but, first, however, lastly, second, so, still, then, while, for example
Attributes: Values AverageValues Percentages(Values/AverageValues)% => Comments
Performance on Part of Speech:
To be verbs : 6.0 10.4613686534 57% => More to be verbs wanted.
Auxiliary verbs: 7.0 5.04856512141 139% => OK
Conjunction : 9.0 7.30242825607 123% => OK
Relative clauses : 6.0 12.0772626932 50% => More relative clauses wanted.
Pronoun: 16.0 22.412803532 71% => OK
Preposition: 42.0 30.3222958057 139% => OK
Nominalization: 3.0 5.01324503311 60% => More nominalizations (nouns with a suffix like: tion ment ence ance) wanted.
Performance on vocabulary words:
No of characters: 1517.0 1373.03311258 110% => OK
No of words: 297.0 270.72406181 110% => OK
Chars per words: 5.10774410774 5.08290768461 100% => OK
Fourth root words length: 4.15134772569 4.04702891845 103% => OK
Word Length SD: 2.51370197887 2.5805825403 97% => OK
Unique words: 164.0 145.348785872 113% => OK
Unique words percentage: 0.552188552189 0.540411800872 102% => OK
syllable_count: 456.3 419.366225166 109% => OK
avg_syllables_per_word: 1.5 1.55342163355 97% => OK
A sentence (or a clause, phrase) starts by:
Pronoun: 0.0 3.25607064018 0% => OK
Article: 2.0 8.23620309051 24% => OK
Subordination: 0.0 1.25165562914 0% => More adverbial clause wanted.
Conjunction: 1.0 1.51434878587 66% => OK
Preposition: 5.0 2.5761589404 194% => OK
Performance on sentences:
How many sentences: 17.0 13.0662251656 130% => OK
Sentence length: 17.0 21.2450331126 80% => The Avg. Sentence Length is relatively short.
Sentence length SD: 38.3927076409 49.2860985944 78% => OK
Chars per sentence: 89.2352941176 110.228320801 81% => OK
Words per sentence: 17.4705882353 21.698381199 81% => OK
Discourse Markers: 4.23529411765 7.06452816374 60% => More transition words/phrases wanted.
Paragraphs: 4.0 4.09492273731 98% => OK
Language errors: 0.0 4.19205298013 0% => OK
Sentences with positive sentiment : 4.0 4.33554083885 92% => OK
Sentences with negative sentiment : 7.0 4.45695364238 157% => OK
Sentences with neutral sentiment: 6.0 4.27373068433 140% => OK
What are sentences with positive/Negative/neutral sentiment?
Coherence and Cohesion:
Essay topic to essay body coherence: 0.212130639261 0.272083759551 78% => OK
Sentence topic coherence: 0.0711992090727 0.0996497079465 71% => OK
Sentence topic coherence SD: 0.0491675446183 0.0662205650399 74% => OK
Paragraph topic coherence: 0.134334028722 0.162205337803 83% => OK
Paragraph topic coherence SD: 0.0531767918773 0.0443174109184 120% => OK
Essay readability:
automated_readability_index: 11.4 13.3589403974 85% => Automated_readability_index is low.
flesch_reading_ease: 62.68 53.8541721854 116% => OK
smog_index: 3.1 5.55761589404 56% => Smog_index is low.
flesch_kincaid_grade: 8.7 11.0289183223 79% => OK
coleman_liau_index: 12.06 12.2367328918 99% => OK
dale_chall_readability_score: 8.52 8.42419426049 101% => OK
difficult_words: 76.0 63.6247240618 119% => OK
linsear_write_formula: 7.5 10.7273730684 70% => OK
gunning_fog: 8.8 10.498013245 84% => OK
text_standard: 9.0 11.2008830022 80% => OK
What are above readability scores?
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Rates: 78.3333333333 out of 100
Scores by essay e-grader: 23.5 Out of 30
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Note: the e-grader does NOT examine the meaning of words and ideas. VIP users will receive further evaluations by advanced module of e-grader and human graders.